Robert A. Millikan and Harvey Fletcher performed the oil drop experiment.
The nucleus of a atom contains the protons and the neutrons all most all of the atoms mass is weigh by the protons and the neurons.
I can think of 2 off the top of my head first is friction and second is gravity
Chlorine has a charge -1. It means that X is +2 so that the formula is XCl2. Group 2 is the correct answer.
Electrons are either lost gained or shared in chemical reactions :)
